CMOS image sensors generally comprise an array of pixels each having a pinned photodiode that accumulates charge during an integration period. The accumulated charge is then transferred to a sensing node of the pixel before being read. The sensitivity of such a circuit, as well as its dynamic range, is at least partially dependent on the size of the capacitance of the sensing node. Indeed, a relatively low capacitance level leads to a high sensitivity, but a low dynamic range. A relatively high capacitance level leads to a high dynamic range, but a low sensitivity.
It is a continuing challenge in the field of image sensors to provide pixels having both a high sensitivity and a high dynamic range, without greatly increasing the size or energy consumption of the image sensor.